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Councils in Auckland and Sydney tackle urban tree decline

Sydney’s Northern Beaches Council and the Waitemata District Council in New Zealand might be oceans apart, but they do share a common concern – the decline of their urban tree canopy due to growing populations and overdevelopment.

Research conducted by Greater Sydney Commission in 2017 showed that some of Sydney’s leafiest areas including Warringah, Hornsby and Willoughby have seen the highest percentage of loss in their urban tree canopy.

Similarly, Waitemata, just north of Auckland in New Zealand, has lost almost 13,000 trees between 2006 and 2016, due to increased private land ownership and high development rates. To combat the decline of their urban forests, local governments are exploring new ways to revive urban greenery in cities.

Auckland greening initiatives

Auckland City Council has launched a new program called ‘urban ngahere,’ meaning ‘network of trees’, which aims to increase city greenery by up to 30 per cent. The program coordinates planting initiatives with members of the local community – like schools, farmers, developers and social groups – to plant and maintain trees across Auckland. These efforts are complimented by a three-pronged strategy that includes interpreting data around tree loss, growing canopy and protecting trees from pests and diseases.

John Mauro, the council’s chief sustainability officer, said that Auckland is one of many large cities under pressure to protect trees against overdevelopment, population growth and other factors like climate change.

“A healthy urban forest enriches our communities, our local economies and our natural environment. Auckland cannot become a world-class city without a great urban forest,” he said.

“Some of the key challenges to our urban forest that we are monitoring include; population growth and urbanisation, ongoing issues with weed and pest control, diseases such as kauri dieback and myrtle rust and factors caused by climate change,” Mr Mauro said.

Another exciting initiative in New Zealand is the Million Trees project, which aims to plant one million native trees and scrubs across Auckland in three years. This partnership between Mayor Phil Goff and the New Zealand Department of Corrections has already facilitated the planting of 750,000 trees to date, with inmates managing tree planting and maintenance.

Sydney greening initiatives

Across the sea, the Sydney Northern Beaches’ Council has joined Auckland City Council in exploring innovative ways to counteract development and increase urban tree canopy.

Compelled by a recent population boom, the council has launched a draft Urban Tree Canopy Plan to protect tree cover in the Sydney Metropolitan area. The plan aims to ease the impacts of Sydney’s growing population by planting 5,000 new trees each year, plus introducing an offset program that will plant two new trees for every one that is removed.

Michael Regan, Northern Beaches Mayor, said the plan will be supported monitoring the tree population, and encouraging support from the Sydney community.

“The immediate focus will be on collating accurate baseline data to allow us to monitor the actions of the plan and ultimately measure how successful we are in protecting and maintaining a healthy and diverse canopy cover,” he said.

“Engaging our community in protecting and enhancing our urban trees will also be a critical factor in achieving the objectives of the Urban Tree Canopy Plan.”

A new video released by Citygreen demonstrates the importance of understanding soils and watering to prevent street tree failure. Citygreen Consultant, Nathaniel Hardy, visits a stressed street tree located in the dry climate of the ACT. Despite being irrigated with a suitably large volume of water, the tree is lacking outer foliage with bare, dead branches clearly visible. So, why is the tree failing to thrive despite receiving the required volume of water?

Nathaniel draws attention to the finely-textured, clay-filled soil in the rectangular garden bed surrounding the tree. A circular mulch ring around the tree is simply not big enough to cope with the volume of water being provided, so much of the water is escaping into the larger garden bed and then onto the surrounding pavement. Because the pavement is only slightly elevated, water does not have a sufficient opportunity to penetrate the fine soil and irrigate the roots below. Instead, we see a dry, caked soil surface which has become largely impervious to water.

As the video demonstrates, simply providing the required volume of water is not enough. Understanding the character of your soil and the runoff behaviour of water provided is integral to providing an environment in which street trees can thrive.

To find out more about Citygreen’s innovative water sensitive urban landscape solutions, visit www.citygreen.com. To speak to Citygreen about this video, email info@citygreen.com.

Trees can be deceiving – while they may look healthy from the outside, inside often tells a very different story. Wood rot in living trees causes overestimates of global carbon pools, timber loss in forestry, and poor tree health. Wood decay is of particular concern in the tropics, with tropical forests estimated to harbor, “96% of the world’s tree diversity and about 25% of terrestrial carbon, compared to the roughly 10% of carbon held in temperate forests.”

But how can foresters and researchers see into a living tree to measure wood decay? Surprisingly, with sound. A recently published article in Applications in Plant Sciences details methods using a sound wave technology called sonic tomography, tested on more than 1800 living trees in the Republic of Panama.

Greg Gilbert, lead author of the article and Professor and Chair of the Department of Environmental Studies at the University of California, Santa Cruz, said, “We don’t yet know where internal decay and damage rank as a cause of tree mortality. Most of the decay is hidden–the tomography now allows us to see how many apparently healthy trees are actually decayed inside.”

Sonic tomography sends sound waves through tree trunks, with the longer it takes for a sound wave to traverse a trunk indicating more decay in the wood. Based on the velocity of sound, the tomograph makes a color-coded image of a cross section of the trunk.

Sonic tomography can also be used for urban forestry. In fact, Gilbert and his colleagues, together with the Smithsonian Tropical Research Institute will collaborate with Panama City to use tomography to evaluate the health and associated risks of Panama’s urban trees.

Winter Park, Florida Goes Out on a Limb:

As with every July, another essential collection of 50-50 matching grants have been issued by the Director of the Florida Forest Service, and the recipients are already endeavoring on essential and compelling projects and initiatives… “to develop or enhance their urban and community forestry programs.”

These essential funds mark the beginning of the third phase of a project to phase out dead or sickly trees with new ones. It is expected that the project’s completion in the Orange County suburb will span across several years.

“The grant was presented to Winter Park for its partial rights of way tree inventory, and this partial inventory will assist the city in managing rights of way maintenance cycles,” as stated in a recent article in the Orlando Centennial.

The Urban Forestry Management Plan confirms, “In 2005, the city hired ArborPro, Inc., a full service urban forestry and software consulting company to perform an inventory of right of way (ROW) trees.” This proactive decision was in part to a devastating hurricane season in 2004, and the canopy is still recovering ten years later. In 2012, a risk assessment study was performed by ArborPro, Inc. on several hundred of those trees.

Fortunately, Winter Park’s Urban Forestry Division seems to be up to the task, and make available for public knowledge their plans and resources on their main webpage. Resources include a robust list of trees ideal for not only creating diversity in the urban canopy, but also the ideal placement of the tree species, such as along streets and sidewalks.

“The city’s urban forest consists of over 75,000 trees on private and public property and there are over 25,000 trees in city rights of way…” and an estimated third of that population will require removal in the next several years. Moving forward, an emphasis will be put on creating more diversity in the tree species, as the tree populace is imbalanced by a majority of mature trees on a decline, making them more susceptible to hurricane damage, disease, and drought.

Though each local community and environment is unique, Winter Park has found the steps towards an attentive, responsible, successful program, and deciding to do so creates a successful future that any urban forest could enjoy.

Ann Arbor Upholds “Tree Town” Nickname:

Most towns and cities have something to boast of, or be known by. The “blueberry capital”, the “garden state”, the “city of love” are all examples, and Ann Arbor’s Michigan is no different. Known as “Tree Town” by its residents, Ann Arbor is true to its nickname. The local community’s action plans and efforts in the local forestry is robust.

In the past year, the City Council adopted a new plan for managing the urban forestry. The plan, “provides policy direction and guidance to city staff on efforts to sustainably maintain and expand the city’s tree canopy. It includes 17 recommendations, including monitoring threats to tree health.”With just under 7,000 trees in parks and over 40,000 trees along city streets, an additional one million dollars was invested in the past year to compensate for backlogged tree maintenance. Other challenges, which are shared by other widespread areas across the United States include the emerald ash borer, which “led to the removal of thousands of ash trees. .”

On the positive side, the value of urban forestry proves itself by a landslide, and it’s estimated that, “Ann Arbor’s publicly managed trees provide more than $4.6 million in benefits to the community each year, including reducing stormwater runoff, saving energy, improving air and water quality, and beautifying the city.”

This 146 page document, the Urban and Community Forest Management Plan includes seventeen “specific recommendations,” including, “Recommendation #11: Enhance and develop programs that encourage active participation by volunteers in the development and promotion of a sustainable urban and community forest.” Actions and resources have thus far followed these intentions, and the City of Ann Arbor webpage cites resources including the 2016 Tree Planting Plan. The tree planting begins this fall of 2015 in November, and spring of 2016.

The clear development of plans, resources, education, and a sense of pride all create a success story for the future of Ann Arbor’s urban forestry. It stands that by following this model, and adjusting to each unique urban forest, other cities, towns, and communities could enhance their tree population’s health and longevity as well. Maybe all our cities could strive to be “Tree Towns.”

What You Need For a Successful Urban Treepit Design:

The benefits that healthy urban trees provide to the environment are significant, but the environmental conditions in urban spaces can often be challenging for their establishment and long-term survival.

In order to provide urban trees with the best chance of survival, it is important to consider the conditions of soil, climate, and water availability that trees face when they are planted in towns and cities. The correct design and installation of tree pits will mitigate the negative effects of the urban environment.

There are several key factors to consider, including root volume availability. The following soil volumes at a minimum are recommended for healthy tree growth:

Small tree 5-15 m³

Medium tree 20-40 m³

Large tree 50+ m³

If in case this amount of space is not available, tree establishment can still happen provided that great care is taken with regard to species selection and root management. In all cases, the deployment of structural root cells can help to prevent soil compaction and ensure that the available rooting volume is fully utilized.

This is very important if the tree is to be located next to a road or another engineered structure, as the soil structure requirements for hard surfaces capable of sustaining large weights are diametrically opposed to those of a healthy tree root network.

Aside from providing sufficient volume for growth for tree roots, it needs to be appropriately directed to ensure that they do not damage surrounding surfaces or underground structures. Paved surfaces and utilities are particularly vulnerable to tree root damage and various types of root management products can be specified depending upon the item that requires protection.

For example, if a tree pit is to be located amidst a continually paved surface then the tree roots will need to be managed downwards by at least 300mm or the depth of the pavement structure to remove the possibility of paving heave.

Next, we’ll discuss more about proper irrigation, drainage and aeration to raise a strong tree network.

The Global Effort to Improve Urban Environments:

It is undeniable how trees in urban environments bring so many benefits to the community. Aside from creating a sense of place, a local identity and a system of landmarks, they also provide space for leisure and community activities, helping residents take pride in the beauty of their location.

A Dutch study said that every 10% increase in green space can postpone health complaints in communities by five years. Because trees filter polluted air, reduce smog, and provide shade from solar radiation, they have been known to help reduce several illnesses.

Mature trees can even have a positive impact on the levels of petty crime and anti-social behavior in inner-city areas. Research conducted in Chicago by scientists from the University of Illinois concluded that even after socio-economic factors were accounted for, the presence of trees in a location could reduce crime levels by as much as 7%.

The impact of mature trees was even more highlighted in individual buildings and developments. An incredible 52% of residents in apartment blocks surrounded by mature trees experienced fewer reported crimes than those without any greenery. And then there are the road safety effects of having trees strategically placed in roadsides. A UK research showed that drivers slowed down in areas with roadside planting and therefore improve pedestrian safety. It also has a calming effect that results in fewer road rage incidents.

Economically, independent studies in the UK and the US show that properties lined with trees are consistently valued between five to 15% higher than identical properties on roads without trees.

These wide range of benefits are causing people to become increasingly aware of the important role of having trees in urban environments as well as their role in creating a sustainable future. Internationally, this is reflected in the number of tree planting commitments being made by leading politicians.

In New York for instance, there are plans to plant one million trees over the next decade, increasing the size of its urban forest by 20%. London aimed to plant 10,000 extra trees across the capital prior to the start of the 2012 Olympics. Another 1 million trees will be planted throughout the UK by the government over the next five years as part of the Big Tree program.

Policy makers are now prioritizing investments in urban forests despite the uncertain economic climate. This is excellent news for environmentalists and regional and urban dwellers.

However, the benefits of these initiatives can only be fully realized if trees planted have the best chance of survival. This means that care must be taken to ensure that they are planted in conditions that allow them to establish and thrive, rather than being starved of nutrients and growing space, particularly rooting volume, because of hostile urban environments.

Studies have shown that inadequate attention to the needs of trees at the early planting stage costs cities around the world millions of dollars per year in repairing damage to pavements, sewers, building foundations, parking lots, and utilities.

Aside from that, trees frequently do not reach their full potential and therefore are unable to do the benefits mentioned above. Next entry, we will tackle the factors that must be accounted for and controlled to provide urban trees with the best possible chances for successful growth and development.

We came across this interesting paper on raising soil levels around trees. The article “Tree Wells” was written by Clifford W. Collier Jr from West Virginia University in the United States. This was first printed in 1968.

This is an extremely difficult job to do without compromising the tree’s health, but you may find some valid tips in this article. Obviously, every project is different, and the usual recommendations apply regarding consultation with a certified arborist.

Changing the original grade around trees can cause severe injury and in many instances result in the death of trees. Damage to the trees may not show immediately, and several months, a year, or even longer may pass before outward signs of injury are visible. How long before injury begins to show will depend upon the age and species of the tree and the depth of change made in the grade. When signs of injury do appear, the damage is generally too great to save the tree.

Raising the Grade

Raising the soil level around a tree is the most serious grade change. Air circulation is cut off and moisture and nutrients cannot reach the tree roots. In some cases drainage is greatly impaired and the tree drowns.

When the roots are covered too deeply, the first sign of suffocation is generally wilting and defoliation, and the bark begins to decay where soil comes in contact with the tree trunk. The tree may then die slowly or all at once.

Generally, the original grade may be increased 4 to 6 inches a year without damaging the tree.

However, if the grade is to be increased a total of more than 18 inches, a tree well will be needed. A good garden soil, rich in organic matter, should be used for the fill.

Constructing the Tree Well

The prime considerations in constructing tree wells are: (1) air circulation in the root area, (2) water and plant nutrients, (3) proper drainage.

Air Circulation

The best way to insure good air circulation is to pile stone completely over the roots of the tree, as shown in Figures 1, 2, and 3. The stone should extend from the well or tree trunk past the drip line. Figure 1 illustrates the use of vertical drain tile spaced at 6-foot intervals around the drip line of the tree.

Fertilizing and Watering

Supplemental water and plant nutrients can be supplied to the root system through the air vents and drainage system. Supplemental leaf feedings with liquid fertilizers will greatly benefit the tree.

Drainage

Proper drainage is vital to the life of the tree. If the original grade drains properly, an extensive drainage system may not be required. A layer of rock and gravel placed over the entire root system to a depth of 1 to 2 feet should be adequate. If extensive alterations in the grade are made and water does not drain properly, a system of drain tile will be needed, as shown in Figure 4. Make certain that the excess water drains completely from the site, or wet spots may occur in other locations resulting in new problems. Also, make certain that the tile extends through the wall to insure drainage from within the well.

NOTE: Cover all tree wells with a screen or decking to prevent children and small animals from falling into the well and to keep debris from collecting in the well. There are several methods of constructing tree wells, which will provide for air circulation, moisture control, and methods of feeding the tree. There are also many variations of these methods.

The method used will depend upon the value of the tree, the amount of work involved, and the cost.

Tree wells may be constructed of field stone or they maybe permanent, masonry-type walls constructed of brick or other material. In either case, the well should be built before the grade is changed because construction is easier, installation of drain tile simplified, and the well will provide extra protection for the tree against other construction damage.

Size of the Well

A tree well should extend a minimum of 3 feet from the trunk of the tree. The greater the diameter of the well, however, the better the chance of saving the tree. The recommended height for tree wells is 3 feet. Deeper wells have been constructed, however, and have been successful. The additional expense and effort involved is easily justified by the value of the trees and the contribution it makes to the landscape.

Decreasing the Grade

Saving a tree when the grade is to be decreased is not as difficult as when the grade is increased. Move out from the trunk of the tree as far as possible (beyond the drip line is desirable), cut the roots of the trees with a sharp spade or saw, and remove the soil with hand tools to the proper depth. A grader can than remove the rest of the soil without tearing the roots. The crown of the tree should be reduced by 1/3 to compensate for the loss of roots.

A retaining wall should then be built around the tree. Make certain that the wall drains properly. Weep holes every 2 feet are generally sufficient. Gravel placed immediately behind the wall also aids in drainage. The tree should be watered and fertilized the same as if it were growing in the lawn.